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Physiological levels of human fibrinogen markedly inhibited the chemotactic activity of human neutrophils triggered by zymosan-activated serum (ZAS), C5a, or IL-8 in a Boyden chamber assay. Fibrinogen also slightly inhibited theN-formyl-methionyl leucyl-phenylalanine (FMLP) -induced migration of human neutrophils. Albumin was devoid of the inhibitory activities displayed by fibrinogen in this system. The inhibition of chemotaxis by fibrinogen was dose-dependent and saturable. Fibrinogen placed in the upper compartment of the Boyden chamber produced a larger inhibition than that obtained with fibrinogen placed in the lower compartment. Lysine as well as the lysine analog 6-aminohexanoic acid (AHA) decreased the inhibitory capacity of fibrinogen. In contrast, both arginine and glutamine failed to suppress the fibrinogen-mediated inhibition of neutrophil chemotaxis. AHA counteracts the inhibition of ZAS-induced chemotaxis by anti-CD18 monoclonal antibody, suggesting that lysine binding sites are required for integrin function in chemotaxis. Fibrinogen also inhibited, in a dose-dependent manner, the oxygen consumption of neutrophils activated by opsonized zymosan. Taken together, the present results indicate that fibrinogen modulates neutrophil functions and suggest that in addition to its role in blood coagulation, circulating fibrinogen may be involved in regulation of the inflammatory response.

The polymerized β-lactam antibiotic ampicillin inhibits the proteolytic activity of human plasmin upon 125I-labeled fibrin clots. The inhibition is dose-dependent, with half-maximal inhibition occurring at 1.25 mM of the polymerized antibiotic. Polymerized ampicillin also inhibits binding of plasmin to fibrin, and 38% inhibition of binding occurs at 10 mM of the antibiotic. Furthermore, polymerized ampicillin inhibits the activation of plasminogen by either urokinase-like plasminogen activator (uPA) or tissue type-plasminogen activator (tPA). At 7.5 mM of polymerized ampicillin, the uPA-mediated plasminogen activation is suppressed by 94%, and half-maximal inhibition is obtained at 0.66 mM. The direct activity of uPA on the chromogenic substrate L-pyroglutamyl-glycyl-L-arginine p-nitroanilide hydrochloride (S-2444) is unaffected by polymerized ampicillin levels of up to 10 mM. The inhibitory effects of the polymerized antibiotic on the activation of plasminogen by both uPA and tPA is totally abolished in presence of fibrin. These interactions may serve as a novel model for ligands that enhance the clot-specificity of thrombolytic agents.

The ability of oleic acid to modulate fibrinolysis was measured by following the urokinase-mediated and plasminogen-dependent cleavage of 125I-labelled fibrin clots. Oleic acid levels within the physiological range exerted a concentration-dependent inhibition of urokinase-mediated fibrinolytic activity. SDS/PAGE revealed that oleic acid enhances urokinase activity but simultaneously increases the autolytic cleavage of the newly formed low-molecular-mass subunit of plasmin. Oleic acid-induced cleavage of this subunit containing the catalytic site of plasmin was suppressed by the plasmin substrate H-D-valyl-L-leucyl-L-lysine-p-nitroanilide (S-2251) and was prevented by alpha 2-antiplasmin. A concentration-dependent inhibition of the activity of purified plasmin on 125I-labelled fibrin clot was also observed; 93% and 50% inhibition was noted with 150 microM and 32 microM oleic acid respectively. Oleic acid at 200 microM also effectively displaced plasmin prebound to a polylysine-Sepharose column. Examination of the fatty acid specificity showed that a minimal chain length of 16 carbon atoms and the presence of at least one double bond, preferably in a cis configuration, were required for inhibition of the fibrinolytic activity of plasmin. Oleic acid at a concentration that produced only a minimal inhibition of plasmin activity induced a marked inhibition by palmitic acid, while palmitic acid alone is ineffective. The findings suggest that oleic acid stimulates plasminogen activation and modulates the fibrinolytic and autolytic activities of plasmin.

SummaryUrokinase activity was assayed by a two-stage globinolytic method and by a direct chromogenic assay. With both methods, the enzyme activity was found to be inhibited by penicillins. The inhibition by penicillin G, carbenicillin, cloxacillin and penicilloic acid was dose-dependent. The Kj of penicillin G and urokinase with the S-2444 as substrate is 4 mM. This compound exhibited a competitive pattern of inhibition. Ampicillin and 6-amino penicillanic acid failed to inhibit urokinase. These results imply that hydrophobic side chains of penicillins interact with the active site of urokinase. The present observation could be relevant in clinical situation in which high doses of beta-lactam antibiotics could modulate the endogenous fibrinolytic activity of circulating urokinase.